Systems of this type and the corresponding methods find application primarily in the field of material processing by means of laser radiation, for example in the context of removal or modification processes in the printing industry, when perforating films and other industrial processes. However, various applications are also found in metrology and fundamental research. In these cases, a pulsed laser beam is provided by means of the laser, the individual pulses of said laser beam having to be modulated in accordance with the requirements of the respective application.
Specifically, depending on the application for which the laser is used, it may be necessary that the intensity of one or more laser pulses must be varied. Moreover, it may be the case that only certain laser pulses are intended to be directed out of the system. For this purpose, it is known for the laser pulses provided by the laser to be modulated or conditioned in accordance with the respective application by means of a modulator arranged in the beam path of the laser.
As modulators, in general electro-optical modulators such as Pockels cells are provided, for example, to which an electrical modulation voltage is applied on the input side and which enable on the output side an optical modulation of the laser pulses in phase, polarization and/or intensity.
In order to be able to modulate individual or a plurality of laser pulses in a targeted manner in accordance with a corresponding modulation stipulation, it is necessary for the modulation voltage also to be pulsed. Furthermore, the modulation voltage is usually at a comparatively high voltage level that is mostly even in the high voltage range (HV) which can result in problems particularly when generating very short modulation pulses of the modulation voltage. This is because the modulation voltage is generally provided as a continuous voltage by a high voltage source and is converted into a pulsed voltage by the actuation of a high voltage switch connected downstream, in accordance with the modulation stipulation.
What is problematic about such known systems, however, is that, particularly in the case of short switching times, said systems have overall a complex construction, and the switching times also cannot be reduced arbitrarily owing to the structural conditions of the high voltage switches.
This has proved to be disadvantageous particularly in the modulation of laser pulses in ultra-short pulse laser systems such as, for instance, Femtosecond lasers having high repetition rates. The reason for this is that, in a manner governed by the system, the high voltage switches require a certain switching time to switch a voltage from a first voltage level to a second voltage level. Specifically, in ultra-short pulse laser systems, these switching times, also referred to as rise time, are often greater than the pause time between the individual laser pulses. As a result of the excessively lengthy rise times, incorrect modulations of individual or a plurality of laser pulses can therefore occur, which, in material processing, for example, can lead to undesired impairments of the processing result. Moreover, a pulse-accurate setting of each laser pulse during the processing process is not possible.